Knee airbag device and connecting method thereof

ABSTRACT

A knee airbag device includes a column cover that covers a rear end portion of a steering column from below; and an airbag module. The airbag module is disposed in a column lower cover and includes a gas generation portion that generates gas and a knee airbag that is housed in the airbag module in a folded state, and is inflated and deployed by the gas supplied by the gas generation portion. The airbag module is connected to the steering column by a snap-fit action.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a knee airbag device that is inflated anddeployed to restrain knees of an occupant when a vehicle has acollision, and also relates to a method of connecting the knee airbagdevice.

2. Description of the Related Art

Conventionally, various knee airbag devices have been proposed toprotect knees of an occupant. For example, Japanese Patent ApplicationPublication No. 2002-037003 (JP-A-2002-037003) describes a knee airbagdevice in which an airbag module is disposed inside a column cover thatcovers a steering column.

Generally, a steering lock is attached to the steering column above anairbag module in a manner such that the steering lock is housed in thecolumn cover, and the steering lock overlaps with the airbag module whenviewed from above the steering column. Therefore, when the airbag moduleis connected to the steering column, to fit nuts to bolts in a directionfrom above the steering column, the airbag module needs to be connectedto the steering column before the steering lock is fitted to thesteering column. This imposes a restriction on the fitting procedure,and makes the fitting operation complicated.

Furthermore, once the steering lock is fitted to the steering column, itis not possible to remove the airbag module from the steering column(because there is no enough space to place tools in). Therefore, forexample, when the airbag module needs to be removed in order to checkthe airbag module, the entire steering column needs to be removed fromthe vehicle body, and thus, a large-scale operation is required.

When the airbag module is connected to the steering column, the airbagmodule is housed in the column lower cover, and therefore the airbagmodule and the column lower cover closely relate to each other in thefitting operation. Therefore, if it is difficult to connect the airbagmodule to the steering column due to the configuration, it tends to bedifficult to fix the column lower cover, which houses the airbag module,below the steering column.

SUMMARY OF THE INVENTION

The invention relates to a knee airbag device in which an airbag moduleand a column lower cover are easily connected to a steering column, andfurthermore, the airbag module is easily removed from the steeringcolumn, for example, when the airbag module needs be checked. Theinvention also relates to a method of connecting the knee airbag device.

According to a first aspect of the invention, a knee airbag deviceincludes: a column lower cover that covers a rear end portion of asteering column from below; and an airbag module disposed inside thecolumn lower cover when the airbag module is connected to the steeringcolumn. The airbag module includes a gas generation portion thatgenerates gas when the gas generation portion is operated, and a kneeairbag that is housed in the airbag module in a folded state and isinflated and deployed by the gas supplied from the gas generationportion. In the knee airbag device, the airbag module is connected tothe steering column by a snap-fit action.

According to a second aspect of the invention, a knee airbag deviceincludes: a column lower cover that covers a rear end portion of asteering column from below; an airbag module disposed inside the columnlower cover when the airbag module is connected to the steering column;and at least one fixing member that connects the airbag module to thesteering column. The airbag module includes a gas generation portionthat generates gas when the gas generation portion is operated, and aknee airbag that is housed in the airbag module in a folded state and isinflated and deployed by the gas supplied from the gas generationportion. In the knee airbag device, the airbag module is connected tothe steering column by sliding the at least one fixing member.

According to a third aspect of the invention, a knee airbag deviceincludes: a column lower cover that covers a rear end portion of asteering column from below; an airbag module disposed inside the columnlower cover when the airbag module is connected to the steering column;and at least one fixing mechanism that removably connects the airbagmodule to the steering column. The airbag module includes a gasgeneration portion that generates gas when the gas generation portion isoperated, and a knee airbag that is housed in the airbag module in afolded state and is inflated and deployed by the gas supplied from thegas generation portion. In the knee airbag device, the airbag module isfixed to the steering column by operating the at least one fixingmechanism one time, and is released from the steering column byoperating the at least one fixing mechanism one time.

According to the first to third aspects of the invention, when thevehicle has a collision with a collision object, the gas generationportion is operated to generate gas. The generated gas flows into theknee airbag stored in the folded state, and thus, the knee airbag isinflated. Thus, the knee airbag is inflated and deployed toward theknees of the occupant, and the knee airbag restrains and protects theknees of the occupant.

According to the first to third aspects of the invention, the airbagmodule is connected to the steering column by a simple action, and thismakes it possible to very easily connect the airbag module to thesteering column.

As described above, the knee airbag device according to the first tothird aspects of the invention makes it possible to easily connect theairbag module to the steering column.

In the knee airbag device according to the second aspect of theinvention, the airbag module may be snap-fitted to a bracket attached tothe steering column.

Alternatively, in the knee airbag device according to the first aspectof the invention, the airbag module may be fitted to a bracket attachedto the steering column by sliding the at least one fixing member.

Alternatively, in the knee airbag device according to the third aspectof the invention, the airbag module may be fixed to a bracket attachedto the steering column by operating the at least one fixing mechanismone time, and may be released from the bracket by operating the at leastone fixing mechanism one time.

As described above, if the bracket is attached to the steering columnfirst, the steering lock may be attached to the steering column beforethe airbag module is fitted to the bracket, or the airbag module may befitted to the bracket before the steering lock is attached to thesteering column. In other words, there is no restriction on theprocedure for connecting the airbag module and the steering lock to thesteering column.

As described above, according to the aforementioned aspects, there is norestriction on the procedure for connecting the airbag module and thesteering lock to the steering column, and this makes it possible toeliminate the need for making substantial changes in the existingsub-line process for the steering column.

In the knee airbag device according to the aforementioned aspects, thebracket may include at least one urging member. The knee airbag devicemay be designed so that a state of the at least one urging member ischanged, by performing a predetermined operation, from a fixing state inwhich the airbag module is fixed to the bracket to a releasing state inwhich the airbag module is released from the bracket, and changed fromthe releasing state to the fixing state by performing the predeterminedoperation in a reverse order. When the at least one urging member isplaced in the releasing state, the airbag module is placed at a positionat which the airbag module is fitted to the bracket, and after theairbag module is placed at the position, the airbag module is fixed tothe bracket by changing the state of the at least one urging member tothe fixing state.

According to the aforementioned aspect, the bracket attached to thesteering column includes the at least one urging member. With the atleast one urging member, it is possible to fit and remove the airbagmodule to and from the bracket in the manner described below.

First, when the airbag module is fitted to the bracket, the urgingmember is placed in the releasing state by performing the predeterminedoperation. When the urging member is placed in the releasing state, theairbag module is set at the position at which the airbag module isfitted to the bracket. Because the urging member is placed in thereleasing state, and thus the airbag module is not fixed to the bracketyet, the state of the urging member is changed from the releasing stateto the fixing state by a simple action to fix the airbag module to thebracket.

On the other hand, when the airbag module is released from the bracket,the state of the urging member is changed from the fixing state to thereleasing state by performing the predetermined operation in a reverseorder. Thus, it is possible to release the airbag module from thebracket. In other words, even after the airbag module is connected tothe steering column (and even if the steering lock is already fitted tothe steering column), it is possible to easily remove the airbag modulefrom the steering column.

As described above, according to the aforementioned aspects, forexample, when the airbag module needs be checked, it is possible toeasily remove the airbag module from the steering column.

In the knee airbag device according to the aforementioned aspects, anairbag door, which is opened downward in a vehicle-height directiontoward a rear of the vehicle when the knee airbag is inflated, may beintegrated with the airbag module, and an opening portion, which iscovered by the airbag door, may be formed in a lower surface of thecolumn lower cover. Further, when the airbag module is connected to thesteering column, a peripheral portion of the airbag door may bepartially covered by a peripheral edge portion around an opening portionformed in the lower surface of the column lower cover so that theperipheral portion of the airbag door is supported by the peripheraledge portion around the opening portion formed in the lower surface ofthe column lower cover.

According to the aforementioned aspects, the airbag door, which isopened downward in a vehicle-height direction toward a rear of thevehicle when the knee airbag is inflated, is integrated with the airbagmodule. The peripheral portion of the airbag door is partially coveredby the peripheral edge portion around an opening portion formed in thelower surface of the lower column cover when the airbag module isconnected to the steering column. Therefore, an opening load of theairbag door is determined by an overlap area between the peripheralportion of the airbag door and the peripheral edge portion around theopening portion formed in the lower surface of the column lower cover.With this configuration, it is possible to relax requirement forproduction accuracy of the column lower cover, as compared to theconfiguration in which a tear line is provided in the column lower coverso that the column lower cover is torn along the tear line, and aportion of the column lower cover functions as the airbag door.

According to the aforementioned aspect, it is possible to relaxrequirement for the production accuracy of the column lower cover,thereby reducing the production cost accordingly.

The knee airbag device according to the first aspect of the inventionmay further include a cover that covers the column lower cover. In theknee airbag device, a module fitting opening portion, which is largeenough for the airbag module to pass through, may be formed in a lowersurface of the column lower cover, and the module fitting openingportion may be covered by the cover from outside the column lower cover.

According to the aforementioned aspect, the module fitting openingportion, which is large enough for the airbag module to pass through, isformed in the lower surface of the column lower cover, and this makes itpossible to fix the column lower cover below the steering column beforethe airbag module is connected to the steering column. Then, the airbagmodule is connected to the steering column by a simple action throughthe module fitting opening portion, and then, the module fitting openingportion is closed by the cover, thereby completing the operation ofconnecting the knee airbag device.

In the knee airbag device according to the aforementioned aspect, it ispossible to improve protection of the airbag module when the airbagmodule is housed in the column lower cover.

The knee airbag device according to the aforementioned aspect of theinvention may further include a door portion that is manually opened andclosed, and that is provided in a sidewall of the column lower cover.

According to the aforementioned aspect, the door portion that ismanually opened and closed is provided in the sidewall of the columnlower cover, and therefore it is possible to form an access hole byopening the door portion when the column lower cover is fixed below thesteering column, and then the airbag module is connected to the steeringcolumn through the module fitting opening portion by a simple action.Further, it is possible to maintain good exterior appearance of thecolumn lower cover by closing the door portion when the airbag module isconnected to the steering column.

In the knee airbag device according to the aforementioned aspect, it ispossible to maintain good exterior appearance of the column lower cover,and it is also possible to further easily connect the airbag module tothe steering column.

According to a fourth aspect of the invention, a method of connecting aknee airbag device includes: attaching a bracket to a rear end portionof a steering column; snap-fitting an airbag module to the bracket sothat the airbag module is disposed below the steering column; and fixinga column lower cover, which covers the rear end portion of the steeringcolumn from below, below the airbag module in a manner such that aperipheral portion of the airbag door is partially covered by aperipheral edge portion around an opening portion formed in a lowersurface of the column lower cover, and fixing a column upper cover,which covers the rear end portion of the steering column from above,above the steering column. In the knee airbag device, the airbag moduleincludes a gas generation portion that generates gas when the gasgeneration portion is operated, a knee airbag that is housed in theairbag module in a folded state and is inflated and deployed by the gassupplied from the gas generation portion, and an airbag door that isopened downward in a vehicle-height direction toward a rear of a vehicleby an inflation pressure of the knee airbag.

According to a fifth aspect of the invention, a method of connecting aknee airbag device includes: attaching a bracket to a rear end portionof a steering column; fitting an airbag module to the bracket by slidingat least one fixing member that fixes the airbag module to the bracketso that the airbag module is disposed below the steering column; andfixing a column lower cover, which covers the rear end portion of thesteering column from below, below the airbag module in a manner suchthat a peripheral portion of the airbag door is partially covered by aperipheral edge portion around an opening portion formed in a lowersurface of the column lower cover, and fixing a column upper cover,which covers the rear end portion of the steering column from above,above the steering column. In the knee airbag device, the airbag moduleincludes a gas generation portion that generates gas when the gasgeneration portion is operated, a knee airbag that is housed in theairbag module in a folded state and is inflated and deployed by the gassupplied from the gas generation portion, and an airbag door that isopened downward in a vehicle-height direction toward a rear of a vehicleby an inflation pressure of the knee airbag.

According to a sixth aspect of the invention, a method of connecting aknee airbag device includes: attaching a bracket to a rear end portionof a steering column; fitting an airbag module to the bracket byoperating at least one fixing mechanism one time so that the airbagmodule is disposed below the steering column, wherein the at least onefixing mechanism removably fixes the airbag module to the bracket; andfixing a column lower cover, which covers the rear end portion of thesteering column from below, below the airbag module in a manner suchthat a peripheral portion of the airbag door is partially covered by aperipheral edge portion around an opening portion formed in a lowersurface of the column lower cover, and fixing a column upper cover,which covers the rear end portion of the steering column from above,above the steering column. In the knee airbag device, the airbag moduleincludes a gas generation portion that generates gas when the gasgeneration portion is operated, a knee airbag that is housed in theairbag module in a folded state and is inflated and deployed by the gassupplied from the gas generation portion, and an airbag door that isopened downward in a vehicle-height direction toward a rear of a vehicleby an inflation pressure of the knee airbag.

According to the aforementioned methods, it is possible to fit theairbag module to the bracket attached to the steering column, by asimple action. Further, by fixing the column lower cover in a mannersuch that the outer peripheral portion of the airbag door, which ispreviously attached to the airbag module, is partially covered by theperipheral edge portion around the opening portion formed in the columnlower cover, the column lower cover is positioned with respect to theairbag module. Thus, the operation of fixing the column lower cover iseasily performed.

As described above, the method of connecting the knee airbag deviceaccording to the aforementioned aspects makes it possible to easilyconnect the airbag module to the steering column, and further, easilyfix the column lower cover below the steering column.

According to a seventh aspect of the invention, a method of connecting aknee airbag device includes: attaching a bracket to a rear end portionof a steering column; fixing a column lower cover, whose lower surfaceincludes a module fitting opening portion that is large enough for anairbag module to pass through, below the rear end portion of thesteering column; snap-fitting the airbag module to the bracket throughthe module fitting opening portion; and fitting a cover to the columnlower cover from outside the column lower cover so that the modulefitting opening portion of the column lower cover is closed by thecover. In the knee airbag device, the airbag module includes a gasgeneration portion that generates gas when the gas generation portion isoperated, and a knee airbag that is housed in the airbag module in afolded state and is inflated and deployed by the gas supplied from thegas generation portion.

According to an eighth aspect of the invention, a method of connecting aknee airbag device includes: attaching a bracket to a rear end portionof a steering column; fixing a column lower cover, whose lower surfaceincludes a module fitting opening portion that is large enough for anairbag module to pass through, below the rear end portion of thesteering column; fitting the airbag module to the bracket by sliding atleast one fixing member that fixes the airbag module to the bracketthrough the module fitting opening portion; and fitting a cover to thecolumn lower cover from outside the column lower cover so that themodule fitting opening portion of the column lower cover is closed bythe cover. In the knee airbag device, the airbag module includes a gasgeneration portion that generates gas when the gas generation portion isoperated, and a knee airbag that is housed in the airbag module in afolded state and is inflated and deployed by the gas supplied from thegas generation portion.

According to a ninth aspect of the invention, a method of connecting aknee airbag device includes: attaching a bracket to a rear end portionof a steering column; fixing a column lower cover, whose lower surfaceincludes a module fitting opening portion that is large enough for anairbag module to pass through, below the rear end portion of thesteering column; fitting the airbag module to the bracket by operatingat least one fixing mechanism one time through the module fittingopening portion, wherein the fixing mechanism removably fixes the airbagmodule to the bracket; and fitting a cover to the column lower coverfrom outside the column lower cover so that the module fitting openingportion of the column lower cover is closed by the cover. In the kneeairbag device, the airbag module includes a gas generation portion thatgenerates gas when the gas generation portion is operated, and a kneeairbag that is housed in the airbag module in a folded state and isinflated and deployed by the gas supplied from the gas generationportion.

According to the seventh to ninth aspects of the invention, it ispossible to fit the airbag module to the bracket by a simple action,after the column lower cover is fixed below the steering column.

As described above, the method of connecting the knee airbag deviceaccording to the seventh to ninth aspects of the invention makes itpossible to easily connect the airbag module to the steering column.

In the method of connecting a knee airbag device according to theseventh to the ninth aspects of the invention, a door portion that ismanually opened and closed may be provided in a sidewall of the columnlower cover, and the door portion may be opened when the airbag moduleis fitted to the bracket, and closed after the airbag module is fittedto the bracket.

According to the aforementioned aspect, the door portion that ismanually opened and closed is provided in the sidewall of the columnlower cover, and therefore it is possible to form an access hole byopening the door portion when the airbag module is fitted to thebracket. Then, the door portion is closed after the airbag module isfitted to the bracket.

As described above, the method of connecting the knee airbag deviceaccording to the aforementioned aspects of the invention makes itpossible to further easily connect the airbag module to the steeringcolumn.

According to a tenth aspect of the invention, the knee airbag deviceincludes: a column lower cover that covers a rear end portion of asteering column from below; a column upper cover that is fitted to thecolumn lower cover and covers the rear end portion of the steeringcolumn from above; and an airbag module that is disposed inside thecolumn lower cover when the airbag module is connected to the steeringcolumn. The airbag module includes a gas generation portion thatgenerates gas when the gas generation portion is operated, and a kneeairbag that is housed in the airbag module in a folded state and isinflated and deployed by the gas supplied from the gas generationportion. In the knee airbag device, the airbag module is fixed below therear end portion of the steering column. The column lower cover is fixedto the airbag module by hooking the column lower cover to the airbagmodule from below, and is fitted to the column upper cover throughengagement between the column lower cover and the column upper cover.

According to the aforementioned aspect, the column lower cover may befitted to the column upper cover by one action.

According to the aforementioned aspect of the invention, when thevehicle has a collision with a collision object, the gas generationportion is operated to generate gas. The generated gas flows into theknee airbag stored in the folded state, and thus, the knee airbag isinflated. Thus, the knee airbag is inflated and deployed toward theknees of the occupant, and the knee airbag restrains and protects theknees of the occupant.

According to the aforementioned aspect, it is possible to fix the columnlower cover to the airbag module by hooking the column lower cover tothe airbag module from below, and fit the column lower cover to thecolumn upper cover through engagement between the column lower cover andthe column upper cover. This makes it possible to very easily fit thecolumn lower cover to the airbag module and the column upper cover.

As described above, the knee airbag device according to theaforementioned aspect of the invention makes it possible to easily fixthe column lower cover below the steering column.

According to an eleventh aspect of the invention, a method of connectinga knee airbag device includes: attaching a bracket to a rear end portionof a steering column; fitting an airbag module to the bracket; andengaging a column lower cover, which covers the rear end portion of thesteering column from below, with at least one engagement portionprovided in the airbag module, and fitting the column lower cover to acolumn upper cover, which covers the rear end portion of the steeringcolumn from above, through engagement between the column lower cover andthe column upper cover. In the knee airbag device, the airbag moduleincludes a gas generation portion that generates gas when the gasgeneration portion is operated, and a knee airbag that is housed in theairbag module in a folded state and is inflated and deployed by the gassupplied from the gas generation portion.

As described above, the method of connecting the knee airbag deviceaccording to the aforementioned aspect makes it possible to easily fixthe column lower cover below the steering column, because it is possibleto engage the column lower cover with the engagement portion provided inthe airbag module by one action, and fit the column lower cover to thecolumn upper cover by one action through engagement between the columnlower cover and the column upper cover.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further objects, features and advantages of theinvention will become apparent from the following description ofpreferred embodiments with reference to the accompanying drawings,wherein like numerals are used to represent like elements and wherein:

FIG. 1 is a partially exploded perspective view showing an entireconfiguration of a knee airbag device and a connecting method thereofaccording to a first embodiment;

FIG. 2 is an enlarged perspective view of a main portion, which shows anairbag module and a bracket when a fitting portion of the airbag moduleis not inserted through a fitting hole of the bracket;

FIG. 3A is a partially enlarged plan view showing a spring member in areleasing state;

FIG. 3B is a partially enlarged plan view showing the spring member in afixing state;

FIG. 4 is a sectional view taken along a vehicle-width direction, whichshows an airbag door and a column lower cover that are engaged with eachother when the airbag module is connected to a steering column;

FIG. 5 is a partially exploded perspective view showing a comparisonexample, FIG. 5 corresponding to FIG. 1;

FIG. 6 is a partially exploded perspective view showing an entireconfiguration of a knee airbag device and a connecting method thereofaccording to a second embodiment; and

FIG. 7 is a sectional view taken along the vehicle-width direction,which shows an entire configuration of a knee airbag device and aconnecting method thereof according to a third embodiment when a columnupper cover is separated from a column lower cover.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment

Hereinafter, a knee airbag device according to a first embodiment of aknee airbag device and a connecting method thereof will be describedwith reference to FIG. 1 to FIG. 5. In FIG. 1 to FIG. 5, the arrow FRindicates the front of a vehicle. The arrow UP indicates the top of thevehicle. The arrow IN indicates the inside of a vehicle in avehicle-width direction.

FIG. 1 is a partially exploded view showing an entire configuration of aknee airbag device 10 according to the first embodiment. As shown inFIG. 1, a knee airbag device 10 is disposed below a rear end portion ofa steering column 12. A combination switch 14 is disposed on the rearend portion of the steering column 12. Further, a steering lock 16 thatprojects outward in a vehicle-width direction is disposed at a positionahead of the combination switch 14 in the direction of the axis of thesteering column 12 with a predetermined space therebetween.

A bracket 18 is disposed between the combination switch 14 and thesteering lock 16 disposed on the steering column 12. The bracket 18includes an upper bracket portion 18A that extends perpendicular to anaxial direction of the steering column 12, and a lower bracket portion18B that extends in parallel with the axial direction of the steeringcolumn 12, from a lower edge of the upper bracket portion 18A. That is,the bracket 18 is L-shaped in a side view. The bracket 18 is made ofmetal, and the upper bracket portion 18A includes a circular throughhole 20. The steering column 12 is inserted through the insertion hole20 and welded to the insertion hole 20, so that the bracket 18 is fixedto the rear end portion of the steering column 12 at a predeterminedposition.

The lower bracket portion 18B is configured to be a rectangular flatplate when viewed from above the steering column 12. The lower bracketportion 18B projects for a predetermined length from the steering column12 in the vehicle-width direction, when viewed from above the steeringcolumn 12. Further, a pair of right and left fitting holes 22 is formedin the lower bracket 18 b at positions on the sides of the steeringcolumn 12. A pair of front and rear hook-shaped nail portions 24 standsoutside each of the fitting holes 22 in the vehicle-width direction sothat the nail portions 24 face each other in a longitudinal direction ofthe vehicle. The nail portions 24 are formed by means of cutting andbending. Further, a raised portion 26 in a linear shape is formedoutside each pair of the nail portions 24 in the vehicle-widthdirection. The raised portion 26 is formed by means of embossing. Theraised portion 26 is formed in parallel with an outer edge of the lowerbracket portion 18B in the vehicle-width direction, and is slightlylonger than the distance between the pair of the nail portions 24. Theraised portion 26 is raised upward toward the steering column 12, andhas a hemispherical cross-section.

The bracket 18 is provided with a pair of right and left spring members28. The right and left spring member 28 function as urging members, andcorrespond to the right and left fitting holes 22, respectively. Each ofthe spring members 28 is formed by a wire, and has a substantiallymountain shape when the spring member 28 is in a natural state. Further,each of the spring members 28 includes a curved top portion 28A, a pairof leg portions 28B, and a pair of folded portions 28C. The top portion28A has an arc shape. The leg portions 28B extend from the top portion28A to form oblique sides of the mountain-shaped spring member 28. Thefolded portions 28C are formed by folding edge portions of the legportions 28B in U-shape.

The leg portions 28B of each spring member 28 are engaged, in anelastically deformed state, with the front and rear nail portions 24provided on the bracket 18. Therefore, the spring member 28 has elasticrestoring force that acts in a direction in which the leg portions 28Bare separated from each other. Further, when the leg portions 28B areengaged with the respective nail portions 24, the leg portions 28B aredisposed in substantially parallel with each other, and the top portion28A is movable with respect to the fitting hole 22, in a directionindicated by an arrow A shown in FIG. 3A. A moving stroke of the springmember 28 with respect to the fitting hole 22 is set to a distancebetween a releasing position (shown in FIG. 3A) at which the foldedportions 28C are engaged with the respective nail portions 24 and afixing position (shown in FIG. 3B) at which the folded portions 28C abutthe raised portion 26. Further, when the spring member 28 is slid towardthe releasing position, the top portion 28A of the spring member 28radially expands so that the top portion 28A overlaps with a peripheraledge portion around the fitting hole 22 (see FIG. 3A).

The knee airbag device 10 fitted to the aforementioned bracket 18includes, as main components, an airbag module 30 that constitutes amain body portion of the knee airbag device 10, and an airbag door 32that covers a lower surface of the airbag module 30.

The airbag module 30 includes an inflator 34 that functions as a gasgeneration portion disposed below the rear end portion of the steeringcolumn 12 when the airbag module 30 is connected to the steering column12, and a knee airbag 36 disposed in a folded state at a position aheadof the inflator 34. The inflator 34 is substantially cylinder-shaped,and the inflator 34 is disposed in a manner such that the longitudinaldirection of the inflator 34 matches the vehicle-width direction. Itshould be noted that the inflator 34 may be a gas cylinder that containshigh-pressure gas. Alternatively, the inflator 34 may contain a gasgeneration agent that generates gas when burned. Further, the kneeairbag 36 is accordion-folded. However, the knee airbag 36 need notnecessarily be accordion-folded. The knee airbag 36 may be rolled up.Alternatively, a portion of the knee airbag 36 may be accordion-folded,and another portion of the knee airbag 36 may be rolled up. The inflator34 and the folded knee airbag 36 provided in the airbag module 30 arecovered by a protective cloth 38 to maintain the shape.

The airbag door 32 includes a door main body 32A disposed under a lowersurface of the airbag module 30, a hinge portion 32B standing from arear edge of the door main body 32A along the inflator 34, an uppersurface portion 32C that extends from an upper edge of the hinge portion32B toward a front side of the vehicle for a predetermined length. Theupper surface portion 32C of the airbag door 32 includes a pair ofinsertion holes 42 with respective slits 40. A pair of left and rightfitting portions 44 (which will be described later) is inserted throughthe pair of insertion holes 42.

The left and right umbrella-shaped fitting portions 44 stand on an upperportion of an outer periphery of the inflator 34 when the airbag module30 is connected to the steering column 12. Each of the fitting portions44 includes a protrusion portion 44A that has a substantially circularcone shape with a flat top surface and that protrudes in a substantiallyumbrella shape toward the steering column 12, and a neck portion 44Bthat is a straight stick member, and that is disposed at an axial centerof the protrusion portion 44A. As shown in FIG. 3B, an outer peripheralradius r1 of a lower end portion 44A′ of the protrusion portion 44A isset to be slightly smaller than an inner peripheral radius R1 of thefitting hole 22, and is set to be larger than an inner peripheral radiusR2 of the top portion 28A of the spring member 28 in the fixing state.Further, an outer peripheral radius r2 of the neck portion 44B is set tobe slightly smaller than the inner peripheral radius R2 of the topportion 28A of the spring member 28 in the fixing state. In the firstembodiment, the outer peripheral radius r2 of the neck portion 44B isset to be slightly smaller than the inner peripheral radius R2 of thetop portion 28A of the spring member 28. However, the inner peripheralradius R2 of the top portion 28A of the spring member 28 may be set tobe substantially equal to the outer peripheral radius r2 of the neckportion 44B.

As shown in FIG. 1, the aforementioned airbag module 30 is covered by acolumn cover 46 that covers the rear end portion of the steering column12. The column cover 46 is made of resin, and is divided into twoportions, i.e., an upper portion and a lower portion. More specifically,the column cover 46 includes a column upper cover 50 and a column lowercover 48. An opening portion 52 in a rectangular shape is formed in alower surface 48A of the column lower cover 48, and the size of theopening portion 52 is substantially equal to the size of the door mainbody 32A of the aforementioned airbag door 32. As shown in FIG. 4, thedoor main body 32A of the airbag door 32 includes an outer peripheralportion 32A′ that is stepped so that the stepped outer peripheralportion 32A′ is engaged with a peripheral edge portion 52A around theopening portion 52. The stepped outer peripheral portion 32A′ of thedoor main body 32A is configured so that when the column lower cover isfixed, the peripheral edge portion 52A around the opening portion 52formed in the lower surface 48A of the column lower cover 48 supportsthe outer peripheral portion 32A′ of the door main body 32A from below.

Advantageous Effects Obtained in the Embodiment

Next, a method of connecting the knee airbag device 10 according to theembodiment to a vehicle will be described. In the description of themethod, the advantageous effects obtained in the embodiment will bedescribed.

First, in a bracket attachment process, the bracket 18 is attached tothe rear end portion of the steering column 12 at a predeterminedposition. More specifically, the right and left spring members 28 arepreviously attached to the bracket 18. Next, the rear end portion of thesteering column 12 is inserted through the through hole 20 formed in theupper bracket portion 18A, and a peripheral edge of the through hole 20of the upper bracket portion 18A is fixed to the outer peripheralsurface of the steering column 12 at a predetermined position of thesteering column 12, for example, by welding.

Next, in a module fitting process, the airbag module 30 as shown in FIG.1 is fitted to the bracket 18 by a snap-fit action. More specifically,the spring members 28 attached to the bracket 18 are placed in thereleasing state (that is, the state indicated by the solid line in FIG.3A). In other words, each of the spring members 28 is slid inward in thevehicle-width direction until the folded portions 28C of the springmember 28 are engaged with the respective nail portions 24. In thisstate, the top portion 28A of the spring member 28 is expanded outwardin a manner such that the top portion 28A substantially overlaps withthe inner peripheral edge of the fitting hole 22. In this state, each ofthe fitting portions 44 of the airbag module 30 is inserted through thecorresponding fitting hole 22 and through the top portion 28A of thecorresponding spring member 28. Then, the spring member 28 is slid untilthe folded portions 28C of the spring member 28 abut the raised portion26 of the bracket 18 using the elastic restoring force of the expandedtop portion 28A. Thus, the spring member 28 is placed in the fixingstate as shown by the chain double-dashed line in FIG. 3A, and the topportion 28A of the spring member 28 is engaged with the neck portion 44Bof the corresponding fitting portion 44 (in other words, theumbrella-shaped protrusion portion 44A of the fitting portion 44 iscaught between the pair of the leg portions 28B of the spring member 28and cannot pass through the fitting hole 22). Consequently, the fittingportions 44 cannot be removed from the spring members 28, and thus, theairbag module 30 is fixed to the bracket 18.

Next, in a column cover fitting process, the column upper cover 50 isfixed above the rear end portion of the steering column 12, and then thecolumn lower cover 48 is fixed to the column upper cover 50 from belowthe steering column 12 to complete the column cover 46. Because theairbag door 32 is attached to the airbag module 30 that is fitted to thebracket 18 prior to this column cover fitting process, the column lowercover 48 is fitted to the airbag module 30 in a manner such that theouter peripheral portion 32A′ of the airbag door 32 is engaged with theperipheral edge portion 52A around the opening portion 52 formed in thecolumn lower cover 48, and thus the airbag door 32 is partially coveredby the column lower cover 48, as shown in FIG. 4.

The steering lock 16 may be fitted to the steering column 12 after thebracket 18 is fixed to the steering column 12, or may be fitted to thesteering column 12 after the airbag module 30 is fitted to the bracket18.

For example, if an electrical system failure occurs in the airbag module30 that is connected to the steering column 12 in a manner describedabove, and a warning message appears on a display portion, such as ameter cluster panel, a driver of the vehicle brings the vehicle to anauto service shop, etc. for a checkup of the airbag module 30. When amechanic performs a checkup of the airbag module 30, it is possible forthe mechanic to easily remove the airbag module 30 from the steeringcolumn 12 by following the aforementioned fitting procedure in a reverseorder. That is, it is possible to easily remove the airbag module 30from the bracket 18 only by changing the state of the spring members 28from the fixing state to the releasing state.

When the vehicle, in which the knee airbag device 10 is provided in theabove-described processes, has a frontal collision (or when it ispredicted that the vehicle will have a frontal collision), a collisiondetection device (not shown) determines that the vehicle has a frontalcollision (or predicts that the vehicle will have a frontal collision),and outputs a detection signal to an airbag ECU. When the airbag ECUdetermines that airbag devices should be operated, a driver seat airbagdevice is operated to inflate a driver seat airbag on the steeringwheel, and the knee airbag device 10 is operated. That is, apredetermined current is supplied to the inflator 34 of the knee airbagdevice 10, and thus, the inflator 34 is operated. As a result, theinflator 34 generates gas, and the gas is supplied to the knee airbag 36stored in the folded state, and thus the knee airbag 36 is inflated.When the inflation pressure of the knee airbag 36, which is applied tothe airbag door 32, reaches a predetermined value, the outer peripheralportion 32A′ of the airbag door 32 is detached (i.e. disengaged) fromthe peripheral edge portion 52A around the opening portion 52 formed inthe column lower cover 48, and thus, the airbag door 32 is openeddownward toward the rear of the vehicle. As a result, the knee airbag 36is inflated and deployed toward the area below the steering column 12and the areas on the sides of the steering column 12. Thus, right andleft side portions, which are disposed between an instrument panel andthe knees of the occupant, receive and protect the knees of theoccupant.

As described above, in the knee airbag device 10 according to the firstembodiment, the bracket 18 is previously fixed to the rear end portionof the steering column 12 at the predetermined position, and then theairbag module 30 is fitted to the bracket 18 by the snap-fit action.Therefore, the operation of fitting the airbag module 30 issubstantially simplified. Consequently, according to the firstembodiment, it is possible to easily connect the airbag module 30 to thesteering column 12.

As a comparison, FIG. 5 shows how an airbag module 62 is fitted, bybolts and nuts, to a bracket 60 that is previously fixed to the steeringcolumn 12. As shown in FIG. 5, if the steering lock 16 is fitted to therear end portion of the steering column 12 prior to the fitting of theairbag module 62, the steering lock 16 overlaps with a position at whichthe airbag module 62 is fastened to the bracket 60 in a plan view.Therefore, although it is possible to fasten a left nut 64 to a leftbolt 66, it is not possible to fasten a right nut 68 to a right bolt 70in FIG. 5. Therefore, after the bracket 60 is fixed to the steeringcolumn 12, the bolts 66, 70 of the airbag module 62 are inserted throughrespective bolt insertion holes 72, 74 formed in the bracket 60 and thenuts 64, 68 are fastened to the bolts 66, 70, respectively, and then,the steering lock 16 is fitted to the steering column 12. Thus, there isa restriction on the fitting procedure. Also, the operation of fasteningthe bolts is complicated, requiring use of some kind of tools.Furthermore, once the steering lock 16 is fixed to the steering column12, the airbag module 62 cannot be removed from the steering column 12because of the steering lock 16.

Compared to the aforementioned bolt-fastened airbag module 62, suchdifficulty in the fitting procedure is eliminated, and it is possible toeasily connect the airbag module 30 to the steering column 12, accordingto the first embodiment. Furthermore, for example, when the checkup ofthe airbag module 30 is performed, it is possible to easily remove theairbag module 30 from the steering column 12 only by sliding the springmembers 28 to change the state of the spring member 28 from the fixingstate to the releasing state. Therefore, it is no longer necessary toperform troublesome processes, such as removal of the entire steeringcolumn 12 from the vehicle. Further, as described above, because thereis no restriction on the procedure for fitting the airbag module 30 andthe steering lock 16, it is not necessary to drastically change theprocedure in the existing sub-line process.

According to the first embodiment, the airbag door 32 is previouslyintegrated with the airbag module 30. Then, when the column lower cover48 is fixed, the outer peripheral portion 32A′ of the airbag door 32 isengaged with the peripheral edge portion 52A around the opening portion52 formed in the lower surface 48A of the column lower cover 48 in amanner such that the outer peripheral portion 32A′ is partially coveredby the peripheral edge portion 52A. Therefore, an opening load of theairbag door 32 is determined by an overlap area between the outerperipheral portion 32A′ of the airbag door 32 and the peripheral edgeportion 52A around the opening portion 52 formed in the column lowercover 48. With this configuration, it is possible to relax requirementfor production accuracy of the column lower cover 48, as compared to theconfiguration in which a tear line is provided in the column lower coverso that the column lower cover is torn along the tear line, and aportion of the column lower cover functions as the airbag door. As aresult, it is possible to reduce production cost of the column lowercover 48 due to the relaxed requirement for production accuracy.

Further, according to the first embodiment, in the module fittingprocess, the airbag module 30 is fitted to the bracket 18. Then, in thecolumn cover fitting process, the column upper cover 50, which coversthe rear end portion of the steering column 12 from above, is fixedabove the steering column 12. Then, the column lower cover 48 is fixedbelow the airbag module 30 in a manner such that the outer peripheralportion 32A′ of the airbag door 32 is partially covered by theperipheral edge portion 52A around the opening portion 52 formed in thecolumn lower cover 48. Therefore, by fixing the column lower cover 48 ina manner such that the outer peripheral portion 32A′ of the airbag door32 is partially covered by the peripheral edge portion 52A around theopening portion 52 formed in the column lower cover 48, the column lowercover 48 is positioned with respect to the airbag module 30. Thus, theoperation of fixing the column lower cover 48 is easily performed. As aresult, according to the first embodiment, it is possible to easilyconnect the airbag module 30 to the steering column 12, and easily fixthe column lower cover 48 below the airbag module 30.

Second Embodiment

Hereinafter, a second embodiment of the invention will be described withreference to FIG. 6. The same and corresponding portions as those of theconfiguration in the first embodiment are denoted by the same referencenumerals, and the description thereof will be omitted.

As shown in FIG. 6, in a knee airbag device 80 according to the secondembodiment, a module fitting opening portion 86, which is large enoughfor the airbag module 30 to pass through, is formed in a lower surface82A of a column lower cover 82. The module fitting opening portion 86 iscovered by a cover 88 that is formed separately from the column lowercover 82. The cover 88 and the column lower cover 82 are connected by astrap (not shown) or the like that functions as a hinge when the kneeairbag 36 is deployed. Further, nails (not shown) are provided atpredetermined positions on four sides of an outer periphery of the cover88 and at predetermined positions in a peripheral edge portion aroundthe module fitting opening portion 86, and thus, the cover 88 is engagedwith the column lower cover 82 through engagement of these nails.

The column lower cover 82 includes right and left sidewalls 82B, andeach of the sidewalls 82B includes a door portion 92 defined by aparting line 90 that extends in a substantially U shape in a side view.The door portions 92 are opened and closed around the respective hinges94 when necessary.

It should be noted that the airbag module 30 is basically configured inthe same manner as in the first embodiment. However, the airbag module30 according to the second embodiment is not provided with the airbagdoor 32 provided in the first embodiment.

Advantageous Effects Obtained in the Embodiment

According to the aforementioned configuration, it is possible to connectthe airbag module 30 to the steering column 12 in a manner describedbelow.

First, in the bracket attachment process, the bracket 18 is attached tothe rear end portion of the steering column 12. Then, in the columnlower cover fitting process, the column lower cover 82 is fixed belowthe rear end portion of the steering column 12. Next, the airbag module30 is inserted through the module fitting opening portion 86 formed inthe lower surface 82A of the column lower cover 82, and the airbagmodule 30 is fitted to the bracket 18 by the snap-fit action asdescribed above.

At this time, the door portions 92 formed in the sidewalls 82B of thecolumn lower cover 82 are opened outward in the vehicle-width direction.Access holes 96 are formed in the sidewalls 82B of the column lowercover 82 by opening the door portions 92, and thus it is possible toeasily fit the airbag module 30 to the bracket 18 by the snap-fitaction. After the airbag module 30 is fitted to the bracket 18, theright and left door portions 92 are closed, and thus, placed in anoriginal state.

Then, as the final step, the module fitting opening portion 86 of thecolumn lower cover 82 is closed by the cover 88.

As described above, according to the second embodiment, it is possibleto fit the airbag module 30 to the bracket 18 by the snap-fit actionafter the column lower cover 82 is fixed below the steering column 12.In other words, the fitting procedure according to the second embodimentis a reverse procedure to the fitting procedure according to the firstembodiment. Generally, if the column lower cover is fixed below thesteering column before the airbag module is connected to the steeringcolumn, the operation of connecting the airbag module to the steeringcolumn tends to be complicated. However, according to the secondembodiment of the invention, the door portions 92, which are opened andclosed, are provided in the sidewalls 82B of the column lower cover 82,and the access holes 96 are formed by opening the door portions 92.Therefore, it is possible to easily connect the airbag module 30 to thesteering column 12. Furthermore, because the door portions 92 are closedafter the airbag module 30 is fitted to the bracket 18, it is possibleto maintain good exterior appearance of the column lower cover 82.

Further, according to the second embodiment, the module fitting openingportion 86 formed in the lower surface 82A of the column lower cover 82is closed by the cover 88. With this configuration, it is possible toimprove protection of the airbag module 30 when the airbag module 30 ishoused in the column lower cover 82. It is a possible option to omit thecover 88 and leave the module fitting opening portion 86 uncoveredbecause the airbag module 30 is covered by the protective cloth 38.However, in this case, the protective cloth 38 is exposed to outsidethrough the module fitting opening portion 86, and this may result indamaging the protective cloth 38 or accelerating deterioration of theprotective cloth 38. According to the second embodiment, however,because the cover 88 closes the module fitting opening portion 86, it ispossible to protect the airbag module 30 (in particular, the knee airbag36) from potential damages.

Third Embodiment

Hereinafter, a third embodiment of the invention will be described withreference to FIG. 7. The same and corresponding portions as those of theconfiguration in the first embodiment are denoted by the same referencenumerals, and the description thereof will be omitted.

As shown in FIG. 7, in a knee airbag device 100 according to the thirdembodiment, it is possible to fit a column lower cover 102 to the airbagmodule 30 and a column upper cover 104 by one action.

More specifically, a plurality of hooks 106 are provided on both sideportions of the airbag module 30 (i.e., sidewalls of a substantiallybox-shaped module casing (not shown) in the vehicle-width direction,which houses the inflator and the knee airbag). The plurality of hooks106 are provided along an axial direction of the steering column 12.

Leg portions 108 corresponding to the aforementioned hooks 106 areintegrally formed in an inner portion of the column lower cover 102. Theleg portions 108 protrude upward toward the steering column 12 for apredetermined length. Each of the leg portions 108 includes arectangular engagement hole 110 at a predetermined position in a heightdirection of the leg portion 108. Thus, the hook 106 is engaged with theleg portion 108 through the engagement hole 110.

Further, engagement nails 112 are integrally formed in inner portions ofupper edge portions of sidewalls 102A of the column lower cover 102 atappropriate intervals. The column upper cover 104 includes engagedportions 114. The engaged portions 114 are recessed portions formed inouter portions of lower edge portions of sidewalls 104A of the columnupper cover 104. The engagement nails 112 are engaged with therespective engaged portions 114.

Advantageous Effects Obtained in the Embodiment

According to the aforementioned configuration, it is possible to easilyfit the column lower cover 102 to the airbag module 30 and the columnupper cover 104 in a manner as described below.

First, in the bracket attachment process, the bracket 18 is attached tothe rear end portion of the steering column 12. Next, in the airbagmodule fitting process, the airbag module 30 including the inflator 34and the knee airbag 36 is fitted to the bracket 18 by the snap-fitaction. Then, the column upper cover 104 is fixed above the rear endportion of the steering column 12 by means of screw-fastening or thelike. Next, in the column lower cover fitting process, the column lowercover 102, which covers the rear end portion of the steering column 12from below, is fitted to the airbag module 30 and the column upper cover104 by one action. More specifically, the hooks 106 provided on thesidewalls of the module casing of the airbag module 30 are engaged, byelastic deformation, with the respective engagement holes 110 of the legportions 108 formed along the right and left sidewalls 102A of thecolumn lower cover 102, and the engagement nails 112 formed on thesidewalls 102A of the column lower cover 102 are engaged, by elasticdeformation, with the engaged portions 114 formed on the column uppercover 104.

As described above, according to the third embodiment, the column lowercover 102 is fixed to the airbag module 30 from below by engaging thehooks 106 of the airbag module 30 with the engagement holes 110 of thecolumn lower cover 102, and the column lower cover 102 is fitted to thecolumn upper cover 104 through engagement between the engagement nails112 and the engaged portions 114 by one action. In this way, the columnlower cover 102 is fitted to the airbag module 30 and the column uppercover 104 by one action, and thus, it is possible to easily fit thecolumn lower cover 102 to the airbag module 30 and the column uppercover 104. As a result, according to the third embodiment, it ispossible to easily connect the column lower cover 102 to the steeringcolumn 12.

Supplementary Description of the Embodiments

(1) In the third embodiment, the column lower cover 102 is fitted to theairbag module 30 and the column upper cover 104 by one action. However,as long as the column lower cover 102 is fitted to the airbag module 30and the column upper cover 104 by engaging the column lower cover 102with the airbag module 30 and the column upper cover 104, the number ofaction(s) may not necessarily be one, and may be more than one.

(2) In the aforementioned embodiments, the spring members 28 that aresubstantially a-shaped when attached to the bracket 18 are employed asurging members. However, the shape and configuration of the spring isnot limited to this, and other springs in different shapes andconfigurations may be employed in the invention. Further, in theaforementioned embodiments, the spring members 28 are configured so thatthe spring members 28 do not apply urging force to the fitting portions44 of the airbag module 30 when the spring members 28 are in the fixingstate as well as when the spring members 28 are in the releasing state.However, the invention is not limited to this configuration, and thespring member 28 may be configured so that the urging force of thespring member 28 is applied to the corresponding fitting portion 44 whenthe spring member 28 is in the fixing state, for example, by setting thedistance between the pair of the leg portions 28B of the spring member28 in the fixing state to be slightly smaller than the diameter of theneck portion 44B. If the urging force of the spring member is applied tothe corresponding fitting portion when the spring member is in thefixing state, the airbag module is stably fitted to the bracket, therebypreventing looseness of the airbag module 30, and further, preventingmisalignment of the airbag module 30 when the knee airbag 36 isdeployed.

(3) In the aforementioned embodiments, the urging members, such as thespring members, are employed to fit the airbag module 30 to the bracket18. However, the invention is not limited to this configuration, and thefitting portions of the airbag module 30 may be fixed and releasedwithout using the urging members, such as the spring members. Forexample, a bracket may include a sliding member, and the airbag module30 may be fixed and released by sliding the sliding members.

1. A knee airbag device, comprising: a column lower cover that covers arear end portion of a steering column from below; an airbag moduledisposed inside the column lower over when the airbag module isconnected to the steering column, the airbag module including a gasgeneration portion that generates gas when the gas generation portion isoperated, and a knee airbag that is housed in the airbag module in afolded state and is inflated and deployed by the gas supplied from thegas generation portion; and a bracket that includes at least one nailportion and at least one urging member, the at least one urging memberbeing capable of temporarily engaging the at least one nail portion, andthe bracket is attached to a rear end portion of the steering column,wherein, the airbag module is moved toward the steering column frombelow and is fitted to the bracket by a snap-fit action.
 2. The kneeairbag device according to claim 1, further comprising: the at least oneurging member that connects the airbag module to the steering column,wherein the airbag module is moved toward the steering column from belowand is fitted to the bracket by sliding the at least one fixing member.3. The knee airbag device according to claim 1, further comprising: theat least one urging member that removably connects the airbag module tothe steering column, wherein the airbag module is moved toward thesteering column from below, and the airbag module is fixed to thebracket by operating the at least one fixing mechanism one time, and isreleased from the bracket by operating the at least one fixing mechanismone time.
 4. The knee airbag device according to claim 1, wherein asteering lock is attached to the steering column above the airbag modulein a manner such that the steering lock is housed in the column cover,and the steering lock overlaps with the airbag module when viewed fromabove the steering column.
 5. The knee airbag device according to claim1, wherein: a state of the at least one urging member is changed, byperforming a predetermined operation, from a fixing state in which theairbag module is fixed to the bracket to a releasing state in which theairbag module is released from the bracket, and changed from thereleasing state to the fixing state by performing the predeterminedoperation in a reverse order; and when the at least one urging member isplaced in the releasing state, the airbag module is placed at a positionat which the airbag module is fitted to the bracket, and after theairbag module is placed at the position, the airbag module is fixed tothe bracket by changing the state of the at least one urging member tothe fixing state.
 6. The knee airbag device according to claim 5,wherein: the airbag module includes at least one fitting portion; thebracket includes at least one fitting hole corresponding to the at leastone fitting portion; the at least one urging member is attached to thebracket in a manner such that the at least one urging member iselastically deformed to have a substantially U-shape, and the at leastone urging member has elastic restoring force that acts to expand the atleast one urging member; the at least one urging member is placed in thereleasing state by moving the at least one urging member in onedirection so that a radius of an inner periphery of the at least oneurging member becomes larger than a maximum radius of an outer peripheryof the at least one fitting portion; and the at least one urging memberis placed in the fixing state by moving the at least one urging memberin an opposite direction to the one direction so that the radius of theinner periphery of the urging member becomes smaller than the maximumradius of the outer periphery of the at least one fitting portion. 7.The knee airbag device according to claim 3, wherein: the airbag moduleincludes at least one fitting portion; the bracket includes the at leastone urging member that is engaged with the at least one fitting portion;and the at least one fitting portion and the at least one fitted portionare fixed to each other by moving the fixing mechanism in one direction,and the at least one fitting portion and the at least one fitted portionare released from each other by moving the fixing mechanism in anopposite direction to the one direction.
 8. The knee airbag deviceaccording to claim 1, wherein: an airbag door, which is opened downwardin a vehicle-height direction toward a rear of a vehicle when the kneeairbag is inflated, is integrated with the airbag module; an openingportion, which is covered by the airbag door, is formed in a lowersurface of the column lower cover; and when the airbag module isconnected to the steering column, a peripheral portion of the airbagdoor is partially covered by a peripheral edge portion around theopening portion formed in the lower surface of the column lower cover sothat the peripheral portion of the airbag door is supported by theperipheral edge portion around the opening portion formed in the lowersurface of the column lower cover.
 9. The knee airbag device accordingto claim 8, wherein: the peripheral portion of the airbag door includesa stepped portion; and the peripheral edge portion around the openingportion formed in the lower surface of the column lower cover is engagedwith the stepped portion in the peripheral portion of the airbag door sothat the peripheral edge portion around the opening portion formed inthe lower surface of the column lower cover supports the stepped portionin the peripheral portion of the airbag door from below.
 10. The kneeairbag device according to claim 1, further comprising: a cover thatcovers the column lower cover, wherein a module fitting opening portion,which is large enough for the airbag module to pass through, is formedin a lower surface of the column lower cover, and the module fittingopening portion is covered by the cover from outside the column lowercover.
 11. The knee airbag device according to claim 10, furthercomprising a door portion that is manually opened and closed, and thatis provided in a sidewall of the column lower cover.
 12. The knee airbagdevice according to claim 1, wherein the bracket includes at least twonail portions and an urging member, wherein at least two portions of theurging member are capable of temporarily engaging the two nail portions.13. The knee airbag device according to claim 1, wherein the at leastone nail portion protrudes from the bracket and the at least one urgingmember has at least one hooked portion, the hooked portion beingconfigured to temporarily engage the at least one nail portion.
 14. Theknee airbag device according to claim 1, wherein the at least one urgingmember is elastically deformable.
 15. A method of connecting a kneeairbag device, comprising: attaching a bracket to a rear end portion ofa steering column, the bracket includes at least one nail portion and atleast one urging member, the at least one urging member being configuredto temporarily engage the at least one nail portion by way of a snap-fitmechanical engagement; moving an airbag module toward the steeringcolumn from below; and snap-fitting the airbag module to the bracket sothat the airbag module is disposed below the steering column, whereinthe airbag module includes a gas generation portion that generates gaswhen the gas generation portion is operated, a knee airbag that ishoused in the airbag module in a folded state and is inflated anddeployed by the gas supplied from the gas generation portion, and anairbag door that is opened downward in a vehicle-height direction towarda rear of a vehicle by an inflation pressure of the knee airbag; andfixing a column lower cover, which covers the rear end portion of thesteering column from below, below the airbag module in a manner suchthat a peripheral portion of the airbag door is partially covered by aperipheral edge portion around an opening portion formed in a lowersurface of the column lower cover, and fixing a column upper cover,which covers the rear end portion of the steering column from above,above the steering column.
 16. The method of connecting a knee airbagdevice according to claim 15, wherein: fitting the airbag module to thebracket by sliding the at least one urging member that fixes the airbagmodule to the bracket.
 17. The method of connecting a knee airbag deviceaccording to claim 15, wherein: fitting the airbag module to the bracketby operating the at least one urging member one time wherein the atleast one fixing mechanism removably fixes the airbag module to thebracket.
 18. The method of connecting a knee airbag device according toclaim 15, wherein the bracket includes at least two nail portions and anurging member, wherein at least two portions of the urging member arecapable of temporarily engaging the two nail portions.
 19. The method ofconnecting a knee airbag device according to claim 15, wherein the atleast one nail portion protrudes from the bracket and the at least oneurging member has at least one hooked portion, the hooked portion beingconfigured to temporarily engage the at least one nail portion.
 20. Themethod of connecting a knee airbag device according to claim 15, whereinthe at least one urging member is elastically deformable.